The present invention relates to color TV circuits.
There are presently several standards for the emission of color TV signals, among which the PAL, NTSC and SECAM standards.
In order to avoid settings by televiewers selecting a specific TV channel without knowing the type of standard of the signal sent on this channel, there are prior art circuits for automatically identifying standards. Under the action of a selection circuit properly conditioning the identification circuit, the latter circuit tests the signal received and, as soon as it has recognized the standard for which it has been conditioned by the selection circuit, it sends control signals to various internal circuits of the TV set for blocking them at the state corresponding to the recognized standard.
On the other hand, some TV sets are designed to receive either TV signals arriving on an antenna, or signals from a video tape recorder.
Conventionally, even though there are two input connectors, one for connecting the antenna and one for connecting the video tape recorder, these two connectors are connected to a same input terminal of the standard identification circuit.
However, nowadays, there is a tendency to develop a new standard for video tape recorder signals, called S-VHS standard. In this standard, the video signal of the video tape recorder is transmitted to the color TV set through two connections. A first cable transmits the color sub-carrier and is connected to a specific input, called S-VHS input, of the TV set. A second cable transmits the luminance and synchronization information and is connected either to the antenna input or to an other usually existing connector (SCART socket).
By separating on two wires the luminance and chrominance information of a video tape recorder, the passband of the luminance signal and therefore a better image definition are obtained.
However, a problem is that the signal arriving on the antenna wire no longer corresponds to any common standard and that the specific connection on which the S-VHS signal arrives is to be selected by a switch. Thus, the user will need an additional control switch for connecting the terminal of the S-VHS signal to the internal circuits of the TV set. This causes several drawbacks. On the one hand, having to actuate an additional manual switch is a constraint for the user whereas, on the contrary, color TV sets are tried to be made more and more easy to use. On the other hand, the provision of an additional manual switch increases the cost of the TV set.
Thus, an object of the invention is to provide an automatic connection of the color TV set to a S-VHS input as soon as a signal occurs on this input.
Another object of the invention is to provide such an automatic connection which increases as little as possible the complexity of the internal circuits of a TV set.